[Bug c/78304] [7 Regression] -Wformat doesn't warn anymore for inttypes.h format string argument type mismatches

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78304

--- Comment #5 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
More notes to self:

The locations within the string_concat_db for this concatenation are all
spelling locations, rather than virtual locations.  The reason is that
c-lex.c's lex_string calls cpp_get_token internally rather than
cpp_get_token_with_location.

I experimented with calling the latter, so that it captures the virtual
location for e.g. PRIu32:

--- a/gcc/c-family/c-lex.c
+++ b/gcc/c-family/c-lex.c
@@ -1150,6 +1157,7 @@ lex_string (const cpp_token *tok, tree *valp, bool
objc_string, bool translate)
      for the common case of just one string.  */
   cpp_string str = tok->val.str;
   location_t init_loc = tok->src_loc;
+  location_t virtual_loc;
   cpp_string *strs = &str;
   location_t *locs = NULL;

@@ -1160,7 +1168,7 @@ lex_string (const cpp_token *tok, tree *valp, bool
objc_string, bool translate)
   bool objc_at_sign_was_seen = false;

  retry:
-  tok = cpp_get_token (parse_in);
+  tok = cpp_get_token_with_location (parse_in, &virtual_loc);
   switch (tok->type)
     {
     case CPP_PADDING:
@@ -1203,7 +1211,7 @@ lex_string (const cpp_token *tok, tree *valp, bool
objc_string, bool translate)

       concats++;
       obstack_grow (&str_ob, &tok->val.str, sizeof (cpp_string));
-      obstack_grow (&loc_ob, &tok->src_loc, sizeof (location_t));
+      obstack_grow (&loc_ob, &virtual_loc, sizeof (location_t));

       if (objc_string)
        objc_at_sign_was_seen = false;

...with that patch, we get the virtual loc encoded within the concat database.
But then this within format_warning_va:
   fmt_loc.get_location (&fmt_substring_loc)
fails, because we don't know how to handle a macro expansion, and doing so
isn't something that seems sane to touch at this point in the development
cycle.

So one (or both?) of the fixes suggested in comment #4 seem appropriate.